On Tue, 24 Jun 2025 at 13:38, Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Mon, Jun 23, 2025 at 08:12:46PM -0700, Kumar Kartikeya Dwivedi wrote:
>
> SNIP
>
> > diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
> > index 75ceb6379368..5fb11202ab9c 100644
> > --- a/kernel/bpf/stream.c
> > +++ b/kernel/bpf/stream.c
> > @@ -2,6 +2,7 @@
> > /* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
> >
> > #include <linux/bpf.h>
> > +#include <linux/filter.h>
> > #include <linux/bpf_mem_alloc.h>
> > #include <linux/percpu.h>
> > #include <linux/refcount.h>
> > @@ -483,3 +484,46 @@ bool bpf_prog_stream_error_limit(struct bpf_prog *prog)
> > {
> > return atomic_fetch_add(1, &prog->aux->stream_error_cnt) >= BPF_PROG_STREAM_ERROR_CNT;
> > }
> > +
> > +struct dump_stack_ctx {
> > + struct bpf_stream_stage *ss;
> > + int err;
> > +};
> > +
> > +static bool dump_stack_cb(void *cookie, u64 ip, u64 sp, u64 bp)
> > +{
> > + struct dump_stack_ctx *ctxp = cookie;
> > + const char *file = "", *line = "";
> > + struct bpf_prog *prog;
> > + int num, ret;
> > +
> > + if (is_bpf_text_address(ip)) {
> > + rcu_read_lock();
> > + prog = bpf_prog_ksym_find(ip);
> > + rcu_read_unlock();
>
> do you need to check prog != NULL ?
I think it should be non-NULL, given we're walking IPs of progs with
an active stack frame so they're not going away.
>
> also is_bpf_text_address calls bpf_ksym_find and bpf_prog_ksym_find calls it again,
> I think it'd be better just to call bpf_prog_ksym_find from here
>
Good point, I will fix that. Then just check it for NULL once and
continue using it.
Thanks!
> jirka
>
>
> > + ret = bpf_prog_get_file_line(prog, ip, &file, &line, &num);
> > + if (ret < 0)
> > + goto end;
> > + ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n %s @ %s:%d\n",
> > + (void *)ip, line, file, num);
> > + return !ctxp->err;
> > + }
> > +end:
> > + ctxp->err = bpf_stream_stage_printk(ctxp->ss, "%pS\n", (void *)ip);
> > + return !ctxp->err;
> > +}
> > +
> > +int bpf_stream_stage_dump_stack(struct bpf_stream_stage *ss)
> > +{
> > + struct dump_stack_ctx ctx = { .ss = ss };
> > + int ret;
> > +
> > + ret = bpf_stream_stage_printk(ss, "CPU: %d UID: %d PID: %d Comm: %s\n",
> > + raw_smp_processor_id(), __kuid_val(current_real_cred()->euid),
> > + current->pid, current->comm);
> > + ret = ret ?: bpf_stream_stage_printk(ss, "Call trace:\n");
> > + if (!ret)
> > + arch_bpf_stack_walk(dump_stack_cb, &ctx);
> > + ret = ret ?: ctx.err;
> > + return ret ?: bpf_stream_stage_printk(ss, "\n");
> > +}
> > --
> > 2.47.1
> >
> >
